On Sat, 31 Aug 2002, Mark D. Studebaker wrote:
> Unlike any other eeprom we've seen, a quick write is not benign
> for these eeproms - it takes it as a start of a write.
> So the following read of chip 0x54 at location 0x48 completes the write
> -
> and location 0xa8 (== 0x54 << 1) gets 0x48 written to it.
> So any read (from any chip!) after a quick write corrupts the chip.
If I understood you correctly, crucial sequence is:
Write Quick "0"
S 0x54 Wr [A] P
Read Byte Data
S 0x54 Wr [A] 0x48 [A] S 0x54 Rd [A] [Data] NA P
Further reads without quick write do not corrupt eeprom ?
And the Write Quick address could be from 0x54 to 0x57 ?
Suppose 24rf08 has a poorly designed state machine that does not check
for Start and Stop conditions right after acknowledging its address.
Below I mark these <S> and <P>, respectively.
The sequence above becomes Write Byte Data + Read Byte. It returns the
data just written in the referenced location (0xa8).
S 0x54 Wr [A] <P><S> 0x54 Wr [A] 0x48 [A] S 0x54 Rd [A] [0x48] NA P
Maybe i2c/doc/smbus-protocol has a typo :
SMBus Write Byte : S Addr Wr [A] Data NA P
IMO : S Addr Wr [A] Data [A] P
Two successive Write Quick "0" become Write Byte, only changing the
reference for Read Byte transactions. This is i2cdetect operation and
causes no corruption.
S 0x54 Wr [A] <P><S> 0x55 Wr?[A] P
If this is the case, latter of the two Write Quick commands is always
acknowledged by 24rf08, and does not reflect a client at that address.
It also means 2 x Write Quick would reset the state machine and prevent
corruption...
> I also repeatedly tried the following things to see if they would
> corrupt the chip,
> nothing did - i2cdetect (which also uses quick write with a 0!),
I know my Matrix Orbital LCD w/ old BIOS forces SCL down forever with
quick write "1" (aka read address). It takes power-off to release it.
> cvs log i2cdetect.c
----------------------------
revision 1.5
date: 1999/07/21 09:35:40; author: kmalkki; state: Exp; lines: +1 -1
(Ky?sti)
* Use write-address to detect devices on the bus.
Simple clients that you can't read, don't ack the read address.
I believe every client has to ack their write address?
----------------------------
--
Ky?sti M?lkki
kmalkki at cc.hut.fi
